Computing circuit for determining bomb release course



A. 23, 12949. s. DARLINGTON 2,479,999

COMPUTING CIRCUIT FOR DETERMINING BOMB RELEASE COURSE Original Filed July 17, 1943 6 Sheets-Sheet 1 FIG. 2 P RP P a n a lNl/ENTOR S. DARL ING TON er I W W ATTORNEY A g- 23, 1949. s. DARUNGTON mmw COMPUTING CIRCUIT FOR DETERMINING BOMB RELEASE COURSE Original Filed July 17, 1943 6 Sheets-Sheet 2 w 44 90 PHASE 2 SH/FIER s. DARL/NGTO/V iii-MAI.

ATTORNEY S. DARLINGTON COMPUTING C IRCUIT FOR DETERMINING BOMB RELEASE COURSE 6 Sheets-Sheet 3 Original Filed July I7, 1943 FIG. /2

$665059 R nv save mum/r09 S. OARL ING TON qrmuw A T TORNE V 1949- s. DARLINGTON 2,479,909

7 COMPUTING CIRCUIT FOR DETERMINING BOMB RELEASE COURSE Original Filed July 17, 1943 6' Shgets-Sheet 4 Y WIND COMPUTER I INVENTOR 1 S. DARL ING TON ATTORNEY Aug. 23, 1949. s. DARLINGTON 2A79 COMPUTING CIRCUIT FOR DETERMINING BOMB RELEASE COURSE Original Filed July 17 '1943 6 Sheets-Sheet 5 lNl/ENTOR 5. DARL l/VG TON By ML ATTORNEY 6 Sheets-Sheet 6 6/75 FILLED DARLINGTON AAAA BOMB RELEASE COURSE COMPUTING CIRCUIT FOR DETERMINING Original Filed July 17, 1943 Patented Aug. 23, 1949 COMPUTING CIRCUIT FOR DETERMINING 130MB. RELEASE JQURSE Sidney Darlington, New York, N. 1., assignor to Hell. eicpiwnc abor o ialncorsflfa si New. York, 3L, a corporation of Original application July L7, 1 943, Serial No, 495,130, new Patent No. 25%39933l, dateQApri]. 13, L948. Divided and this application. April 27; 194.5, SerialNo. 590,603. i w

3 Claims. (Cl.

This invention relatesto a computer associated w aa aer a bom sis t; an bar cu 'a o co puter in which the. datafare represented in In oi electrical quantities. 'Ifhis applion 1s a division oif United States application j"-1 i;."45,130,hiq Julyl'l, 15943 by s. Darlingtonf C. H. Townes and l). E.'Wooldridge patented April 13, 1948, Unitd state's Patent 2,439,- 381.

The object of the inyention is a means for indicating the correct course to be flown by an aerial vehicle, so that the bomb will fall on a target.

Ijhe invention is embodied in an electrical systern whichderives from thasmoothed electrical Quantities representing the components of the g-mundspeea normah'to the vertical 'plane through the bomber and target, and in said plane, another electrical quantity representing the component of=the ground speed normal to the vertical plane containing the axis. of the bomber, modihes; the magnitude of this latter quantity pro nortionally to the ratio. oi the trail, of the bomb to the horizontal rangev to the target, and compares this modified quantity. with said first quanto. he licrizeii a r n e f ac e aiihs the output at the aisslifi r'q r ietall t h tail. of the bomb, and comhaiing the fractionated outsa with $3 54 fir tqua Th P esent 'inr i er as oc ed t a hornbsight capable of continuously measuring an angle and a dis 'nce." The azimuth ear i ceases s s s -a plane at the aerial vehicle to th verticalplan e through the line of slight." 'Thei'efrei'ic' plane may conveniently be taken to bathe vertical plane that includes the li ead-to-tailafin's of the aerial vehicle, and the azimuth angle may be measured clockwise. The distance is the slant distaste" from" the vehiclaor airplane to the target. Thebombsight may be an optical m strum'ent includinga theodolite for measuring the azimuth angle and an optical range finder for measuring thedistan'ce, a'radio locating equipment capable of measuring the azimuth angle mama a P rt o attic su m ro i nal and slant distance or a cornbination of optical and: radio The range finder may also he; to "measure heightor elevation of the :rneht of height, and the continuous easurements of aziniu'th angle and slant dis: tance are; supplied as; 'vo1tages*'to the computer, together information in the form of voltages ffirsiitizig the v'ctofvelocity 6f: the" airplane with respect to the air and the ballistic char' j acterist cs'oi the'bomb used, andthe computer conts y indicates'the correct course to. be sewn, and finally operates release mechanism at the'corr'ect intranets drop the bomb so as to strike 'thtargt. r The operation of the computer will be better understood from the drawings; in which:

"Fig. 'I shows the geometrical relationships, projected on'a horizontal plane through the vehicle:

Fig. 2: shows the geometrical relationshipspro- J'ected on a vertical'plane through the vehicle and the target;

Fig. 3- di'agram-matically shows the vector and oomponentvelocities involved in Fig. 1;

Fig. 4 shOWs' the. geometrical relationships of Fig. 1 at the instant. of release of the bomb;

Fig. 5 shows the velocity relationships of Fig. 3 a the. insta t o re eas o the om 371g. 6 diagrammatically shows a radio locator associated with the com uter;

Fig. 7 schematically shows a device for producinga rotation proportional to horizontal range;

Fig. 8 shows a summingamplifier forming part i he evice shown n Fi Fig. 9. schematically shows a device for producing a rotation proportional to the difference between the angles 0 and X;

Figs. 1;), 11 and 12 schematicallyshow the computing elements forming part of the invention;

Fig. 13 schematically shows a summing amplifier forming part oflfigs. 1Q, :1 and 12;

Figs. 14 and 14A schematically show the circuit for the steering meter; and r Fig. 15 schematically shows the circuit for releasing the bomb.

In Fig. l, P represents an aerial vehicle, such as an airplane, headed along the course A ssume, as usual in bombing technique, that the airplane is flying at' constant speed and at constant height. If a wind be blowing with respect to the target, the airplane will actually travel along a track such as PB; The target is located at'ii, and the function of the present invention is to indicate the correct track PB, and the correct release point RP so that the bomb will fall on the target.

In Fig. 2, the constant height H of the airplane is PD, the constantly measured slant distance p is PO. From these two measurements, the computer can continuously compute the distance D0, which is the horizontal range R, represented by P in Fig. 1.

If PA is a correct bombing course, and the airplane steadily heads along the course PA at constant speed and height, releases a bomb at RP, and continues at the same speed along the track PB, it will reach the point B at the time of impact. The distance 013, along the fore and aft axis of the airplane is known as the trail T, and is tabulated in the ballistic tables for the type of bomb used.

The angle APO between the course of the airplane and the vertical plane through the target is designated 0. If the air structure is standard, the bomb will fall directly behind the airplane, in the vertical plane including the head-to-tail axis of the airplane, that is, the trail is in the line of the course, so that angle BOC=angle APC=0. Thus, 00, the range component of the trail equals T cos 0 and BC, the deflection component of the trail equals T sin 0. The distance PC equals R+T cos 0.

' The airplane is equipped with a gyroscopic device, such as the device shown in United States Patent 1,959.803, May 22, 1934, B. A. Wittkuhns, which maintains an axis PX having a direction fixed in space and is equipped with a servomotor which indicates the angle i between this axis and some fixed axis of the airplane which may conveniently be the head-to-tail axis of the airplane lying in the course of the airplane.

The azimuth angle 0 is continuously measured by the observing equipment, thus, the angle 6,

between the axis fixed in direction and the vertical plane containing the airplane and the target, which is equal to 0- may be determined.

The relative velocity between the airplane and the target, which may be termed the ground speed is indicated by the vector V, Fig. 3. This vector V may be resolved into a component R in the vertical plane containing the airplane and the target. This component is the rate of change in the horizontal range R, indicated by the dot, and as the range is decreasing is inherently a negative quantity. The vector V is also resolved into the component GF, equal to R8. where 5 is the rate of chan e in 6. (This resolution of vectors is shown in section '7, page 7 11, of The Dvnamics and Particles, A. G. Webster, 1912, published by G. E. Stechert and Cornpany, New York.)

In Figs. 1 and 3, the triangles BPC and FPG are similar, thus,

This equation may be multiplied by and rearranged to give R$+-g(R5 cos 0+1? sin 0) =0 1 If a voltage varying in proportion to the lefthand side of Equation 1 be produced and applied to a meter, the needle of the meter will be in the l center of the scale when the airplane is on the correct track; when the airplane is to the right of the correct track, the needle will be deflected to the left of the center of the scale; when the airplane is to the left of the correct track, the needle will be deflected to the right of the center of the scale. The needle of the meter thus indicates in which direction the airplane should be turned to come back to the correct track.

Fig. 4 shows the relationship of Fig. 1 at the instant the airplanev passes through the release point RP. The condition defining a correct release point is that if the plane continues after releasing the bomb along the same track at the same velocity for a time equal to the time of fall t of the bomb, it will just reach a point at a horizontal distance from the target, measured along the line of the course equal to the trail T.

In Fig. 4, as in Fig. 1, angle B00 is a right angle. Then, as before, the distance RPC equals R+T cos 0. The distance RPB is the distance the airplane travels at a velocity V during the time of fall if of the bomb and evidently equals Vt. In Fig. 5 the velocity of the plane V is represented by the vector RPB, and the range component of this velocity R is represented by the vector RPC. In Figs. 4 and 5 the triangles RPBC are similar. Thus R R+ T cos 0 V Vt and

R+Tcos 0+R=0 2 The expression R+T cos 0 is termed the range component of the displacement of the vehicle from its predicted position at the instant of im- The angle 6 is measured with respect to an axis having a direction fixed in space, thus Equation 1 is valid for any course curved or straight. The voltage proportional to Equation 2 decreases as the airplane approaches the release point, and falls to zero at the release point. Thus, during the bombing run, the pilot may fly on any course at the measured height, and the steering meter will indicate the direction to be steered to come to the correct track, while the release meter indicates the time before reaching the correct release point. A convenient time before reaching the release point, the pilot steers to the correct track and follows this track when passing through the release point. After the bomb is released, the pilot may fly on any desired course.

In following a moving target, an observer will tend to overrun and underrun the target with his tracking device, thus introducing errors and irregularities in the data furnished to the computer. To make an accurate determination of R and R6, the derived ratio must be averaged or smoothed. It is very difficult to smooth the measured values of a quantity such as R or R6, the correct value of which is varying. Therefore, in accordance with the present invention, the observed positional data are operated upon so as aeuaaae to yield expressions: for velocity components which are inherently constant, and these quantaties are" averaged. The observed positional: data are operated upon to give the components, parallel' and perpendicular tothe fixed axis, of the vector velocity of the air with respect to-the target; This vector velocity is constant during the bombing runand is therefore appropriate for averaging.

In Fig. 3 the vector S is the vector velocity of the airplane with respect'to the air, measured along the course, or head-to-tail axis of the airplane, by known means, such as a Pitot tube device.

The vector W represents the vector velocity of the air with respect to the target, which is the vector velocity of the wind with respect to the ground minus the vector velocity of the target with respect to the ground.

The vector V represents the vector velocity of the airplane with respect to the target.

These three vectors are not independent but satisfy the relation:

Taking the :1: axis along PX, the axis fixed in space by the gyroscope, and the y axis normal to PX, the vector S may be resolved into the components +SI=+S cos A Sy=-S sin A, in which +5 cos A is the component of the airspeed along the fixed axis, and S sin x is the component of the airspeed transverse to the fixed axis.

In deriving Equation 1, the vector V was resolved into a vector PG designated -R, and a vector GF, designated R8. In Fig. 3 GM and FN are normal to the fixed axis, and FL is normal to GM, thus FL equals MN. The angle PGM equals and as angle PGF is a right angle, angle FGM equals 6. Thus, PM equals R cos 6 and MN equals FL which equals R8 sin 5, thus the component of V along the fixed axis, designated Vx, equals R cos 5+R6 sin 6.

Vy, the component of V transverse to the fixed axis, is FN, which evidently equals GM minus GL; thus Vy equals R sin 6R6 cos 6.

' As W=.S+V, the components of W may be written as WI=-s cos 7\-R cos 5+Ra sin a (3) W.,=+s sin \R sin a Rt cos a (4) or, in the equivalent form W,=S cos lxg flt cos (i) (5) d W,,= +3 5111 (R sin 5) (6) where R dt cos is the ground speed along the x axis, and

d H3 sm 5) v is the ground speed transverse to the :1: axis.

The values of Wx and Wy are averaged for the time Of the bombing run, and in the averaging 6. process the. data.areweightediinproportion to the accuracy of the measurements. I:-,et the a verag e values: of these components; be We and Wy.

From Equations 3' and 4 cos G t-W cos 6+ sin 8. (7)

to -=8 sin 05W; sin 61+-W,,. cos, 5.

where R 'and- R5: 7

are subject to the low inaccuracies of the weighted time averages, of Wx and Wy, and may be used in the computation of the correct course and release. point by Equations 1 and 2.

The present device requires voltages proportional to the slant distance from the. airplane to the target, and to the azimuth angle from the reference. vertical plane to, the vertical plane through the airplane and the target. Many known devices may be adapted to supply these voltages. A potentiometer may be mounted on an optical range finder, and the wiper moved in accordance with the movements of the range indicator to select a voltage proportional to the slant. distance measured by the range finder. An! other potentiometer may be mounted concentrically with the vertical, axis of a theodolite sighted on the target, and the wiper moved in accordance with the rotation of the theodolite to select a voltage proportional to the angle turned by the theodolite. Or, as shown in Fig. 6., a radio locator of any suitable type, such as shown in British Patent 535,120, March 28, 1 941, Com-. pagnie Generals de Telegraphic Sans Fil, may be adapted to supply these voltages. In this particular locator, the range is indicated by the location of a bright spot on the surface of a cathode ray oscilloscope N. A worm shaft ll, rotated by a hand wheel I2, or by a suitable motor, drives a nut I3 carrying a pointer I4 which is kept aligned with the bright spot on the oscilloscope. The winding IQ of a potentiometer is mounted below the Worm shaft ll, the wiper l5 of the potentiometer being mounted upon, but insulated from the nut [3; A suitable source of voltage may be connected to the terminals I6, I1, and the wiper 15 may be led out to a terminal I8. The antennas and reflectors 2|], 2| of the radio transmitter and receiver may be supported by a framework mounted on a shaft 22 journaled in a support 23 rotatably mounted in a base 24. The hand wheel 25, bevel gears 26 and gear 2'! drive the gear 28 rotating the antennas in azimuth. A potentiometer winding 29 may be mounted upon the base 24 but insulated therefrom, and connected to the terminals 30, 3|. A wiper 33 may be mounted upon the support 23 but insulated therefrom and connected to a terminal 32. The voltage selected by the wiper 33 will then be pro portional to the azimuth angle. While, for the sake of explanation, one specific type of locator has been illustrated it is evident that the present invention is not limited to use with such a device, but will operate with many optical, mechanical, radio, sonic and other devices.

In Fig. 7 voltage from a suitable source 35 is applied to the terminals 16, H of the winding l9 associated with the range indicator in Fig. 6. Voltage from the source 35 is applied to the windings 31 and 38 of two other potentiometers. The windings I9, 31, 38 have a resistance per unit length varying linearly with the wiper displacement, so that the voltages selected by the wipers I5, 39, 4B are proportional to the square of the distance moved by the wipers.

The voltage selected by the wiper I5 is, as indicated, of the opposite polarity to the voltages selected by the wipers 39, 40.

The wiper 39 is set at the measured value of the height of the airplane.

The voltages selected by the wipers 39, 40 which are respectively equal to +H the square of the height or altitude of the airplane, and approximately equal to +R the square of the horizontal range, and the voltage from the wiper |5 which, due to the reversal of polarity, is proportional to p the negative square of the slant distance, are respectively supplied to a summing amplifier 4 I, which may be of the type shown in Fig. 8.

It'will be noted from'Fig. '2, that H and R are the sides of a right triangle, of which 1) is the hypotenuse, thus H +R2p should equal zero. If the voltages summed up by the amplifier 4| are not equal to zero, the relay 42 will be operated. The relay 42 is a polar relay, normally biased to a central position, and moved in one direction or the other depending upon the polarity of the applied voltage.

The relay 42 controls the supply and phase of alternating current from the source 43 to one phase of the two-phase motor 46, the other phase of the motor 46 being supplied from the source 43 through the 90-degree phase-shifting network 44. When the relay 42 is operated the motor 46 is started, rotating in a direction related to the polarity of the voltage applied to relay 42. The wiper 40 is moved by the shaft of the motor 46, either directly or through suitable gearing, flex ible shafting or other mechanical expedient. The movement of the wiper 40 changes the Voltage selected by the wiper 40 until the voltage in the output of amplifier 4| is reduced to zero and relay 42 is released. Under this condition and the movement of the wiper 46 indicates the value of R, the horizontal range. Other potentiometers may be mounted so that their wipers will also be rotated by the motor 46 an amount pro portional to R.

, The summing amplifier 4| of Fig. 7, which is shown in Fig. 8 may include any desired number of stages of amplification. Any suitable vacuum tubes may be used, though pentode tubes, .or other tubes of high gain, will generally be found most efiicient. The heaters are supplied with power in known manner (not shown).

The resistors 41, 48, 49 are connected to the control electrode of the vacuum tube 50, the terminal 5| being grounded, The first stage vacuum tube 56 may conveniently be a single cathode double triode, though two separate tubes of any suitable type may be used. The cathode of the vacuum tube 56 is connected to aresistor 52 of fairly high resistance, say of the order; of one or two hundred thousand ohms. The anode current flowing in the resistor 52 would tend to make the cathode of the vacuum tube 50 positive with respect to ground. A source of voltage 53, having the negative pole connected to the resistor 52, and the positive pole connected to ground on terminal 5|, compensates for the voltage drop in resistor 52, so that the cathode of the vacuum tube 50 is at substantially ground potential. Since the total space current leaving the cathode is very nearly equal to the quotient of the voltage of 53 and the resistance of 52, theirrelative 'pled to the vacuum tube 54 by an interstage coupling network of the type shown in United States Patent 1,751,527, March 25, 1930, H. Nyquist, including the resistors 56, 51, 58 and a source of voltage 55 having the positive pole connected to resistor 56, the negative pole connected to resistor 58 and an intermediate point connected to ground. The resistor 56 may be adjustable toassist in making the potential of the cathode of vacuum tube 56 equal to ground potential.

The vacuum tube 54 is coupled by a similar interstage coupling network to the vacuum tube 60.

7 Current from a source 6| is supplied through resistor 62 to the anode of vacuum tube 66, returning through the cathode to the source 65.

The wipers I5, 39, 40, Fig. 7, are respectively connected to resistors 41, 48, 49 and the winding of relay 42 is connected to terminals 43, 64.

The source 6| tends to maintain the terminal 63 at a potential positive with respect to ground. This potential is opposed by a potential from the source 65 through the Winding of relay 42 so that, in the absence of an applied signal, the terminals 63, 64 are at the same potential, that is, there is no potential difierence applied to the winding of the relay 42, Fig. 7. Assume that a voltage is applied to one of the resistors 41, 48 or 49, of such polarity that the amplified voltage causes the control grid of the vacuum tube to become more negative. This voltage will reduce the anode-cathode current of the vacuum tube 66, reduce the voltage drop across the resistor 62, increase the positive potential of the terminal 63 with respect to ground and cause a current to flow from the terminal 63 to the terminal 64 through the winding of the relay 42, Fig. 7, operating the relay 42 in one direction. If the applied voltage is of such polarity that the amplified voltage causes the control grid of the vacuum tube 60 to become less negative, the anode-cathode current of the vacuum tube 60 will increase, increasing thevoltage drop across the resistor 62, reducing the positive potential of the terminal 63 with respect to ground and causing a current to fiow from the terminal 64 to the terminal 63 through the winding of the relay 42, Fig. 7, operating the relay 42 in the other direction.

A portion of the output of the vacuum tube 54 flows through the voltage dividing resistors 66, 6]. A portion of the voltage drop across the resistor 61 is applied by the wire 68 to the control grid of the lower portion of the twin triode 5|]. A source of voltage 69 has the positive terminal connected to the anode of this portion of the twin triode 50 causing a current to fiow from anode to cathode, thence through resistor 52 and source 53 back to source 69. This current flowing in the resistor 52 tends to make the cathode of vacuum tube 56 positive with respect to ground which is equivalent to a negative voltage on the control grid of the upper .portion of the twin triode 50. This added voltage is included in the compensation by the source 53 so that normally the control grid of the upper section and the gathode of the twin triode 50 are at ground p0,-

9 .tential when the two anodeicurrents have reasonable values. The voltage :irom the resistor .61 is .efiectively a negativefeedback tothe control grid :of the upper portion of the .twin triode 50. Assume a voltage is applied through one-of the resistors 41, 48 or 4.9 to make the-control grid of the upper section'of .thetwin triode more negative. The anode-cathode :currentof this section will decrease, decreasing the Voltage .dropin resistor B, makingthe controlzgrid of vacuum tube .54 more positive or .less negative. The anode- .cathode current of vacuumtube-fid will increase, increasingthe voltage'dropin resistor 10 making the controlgrid of vacuum tube 00 .and the con- .trolgr-id of the lower vsection of the twin .triode less positiveor more negative. The anodecathode current of the lower section of the twin triode .50 will increase, decreasing the voltage drop .in the resistor 52, decreasing the positive potential .of thecathode, which is equivalentto .decreasingthe -negative potential to the control gridof the upper section of the twin triode .50. .Then when .theapplied signalmakes thecontrol grid more negative, the.=feedback tends to make thecontrol grid lessnegative and .isthus ,a negative feedback.

It has been shown in United States Patent 2,251,973, August .12, 19.41, .E. .S. .L. .'Beale et .-al,, .forexample, that thelvoltage acrossa capacitor may .be proportional to the time derivative or rate of. changeof the. applied voltage. The capacitor .II differentiates the applied voltage and feeds back -a voltage proportional to the @time derivative .of .the applied voltage which assists in preventing hunting and oscillation .of the. motor A6, Fig. .7.

The source of voltage 52 supplies voltage through .r-esistor 13 t0 the potentiometer T4 to adjust the bias voltages .applied to the control gridso-f the rvacuum tubesfifl and'5.0.

.Fig. -9 shows a .device similar .to the .device shown in.-Fig. .7 to producea rotation of. a. shaft proportional .to the angle dlF'ig. 1. A voltage source I5 is connected across the windings of the .potentiometers "I6, 11. [A .voltagesource 1'8 .is connected across the winding of the poten- ..tiometer..29., which isalso shown inFig. 6. The windingsof the potentiometers I6, I1, 29haveza linear .variation ofresistance .with movementof the wipers. The wiperTS of potentiometer I6 is movedbythe .servomotor of the gyroscope maintaining the fixed axis shownjn'Fig'l through the anglek andselects a voltage proportional to The wiper 3.3 of'thepotentiometer 29 is moved by the antenna support 23, Fig.6, through an angle aandldueto thereversedpolarityof source .18, selects a voltage proportional to ;H. The .potentiometerused in this device maybe the potentiometer ;.Z9 shown in Fig. 6, or a second potentiometer similarly associated .with theantenna support 23. The voltage selectedjbylthe wiper is approximately proportional to'(0-7\) The voltages selected by .the wipers of the potentiometers are supplied to individual input resistors of a summing amplifier 8I, which may be of the type shown in Fig. 8. The-voltage in" the output of the amplifier-81will'be-proportional to \-0+ (0-)0 which should equal zero. If this voltage is not equal to zero, the relay 83 will be operated, starting the motor 82, which moves the wiper 80 of potentiometer""l7 to make the'voltage "from amplifier 81 equal 'to zero, releasing relay 83 and stopping the motor. The-shaft of the motor '82 willthen have moved through an angles-A- which is equal to the-angled,- Fig. 1.

10 Thus, .fromthe antenna support .23 of .Eig. there .is a movement proportional to .the ,angle .0, Fig. l; irom the servomotor of the gyroscope maintaining the .fixed .axis there is .a movement proportional to the angle A, Fig. 1; from theshaft .of the motortz, Fig. 9, there is amovementproportional to era, that is, the angle ,5, Fi .1; and vfrom.theshaftof the .motor 46, Fig. .7, thereima movement-proportional tothe horizontal range R, .2. .It isobvious that more vthan.onepoten .t meter winding may be associated witheach of these devices, so that the wipers will .be moved proportionately tothe particular movement. A

servomotors .may .be geared, or otherwise .001 nected to the shafts, so-that the motor may.mak.e morethan one-revolutionfor onerevolution of the ,W-IIQCI'S.

,InEig.,11,.a.source.of voltage 91 has itspositive .poleconnected to one end of the windingiilflnd its negative groundedpoie connected .to the other end of the .windingsz. Another. sourceo'f voltage 93 has its negative pole connected to one end of the winding 9, 3 and its grounded positive pole connected to theother end of winding ja l. The windings .92, .99 are preferably segments of the same circle, and have a variation of resistance such asto. give a linear variation ,in voltage. The wipers; 95, .95. are movedby. theshaft. of the motor .45, Fig. 7, butare insulated .therefrom and tram eachothento. select voltages, respectively positive and negative, proportional to the horizontal range. R.

The voltages selectedpy the Wipers 05,06 are respectively appliedto twodiametrically opposite points .08, 0,9 .of the .pntentiometer winding "01. .The equidistant, intermediate diametrically Qpp site .points I00, 10] .Qf-the potentiometer windn 1 ar .sonnected to .sround- Th w n in Slhas .a resistance varying with length suchthat the voltageof the winding withrespectto ground varies ,witha sinusoidal ,function. Assuming zero angleat .the point. I00and that the wiper starts at.point I00 .and rotates clockwise, the voltagepf t e wiper withr sp ct to. ground will be ,zeroa point m0, positive maximum .at point .98.. z ro a P in e a ive maximumat point.99, and zero at .point .ilifl .and this is the .varia i npf .a positivesine. If thedirection of the Wi er be turned through degrees, the sign. of the. sine will be reversed. Thus the wiper I02, which is turned through '180 degrees will select a voltage varying with the negative sine ofthe angle of rotation,;andthewiper I03, which leads the-wiper I'02by;9.0 degrees will select a voltage varying withthenegative cosine of the angle of rotation. The wipers ;I02, ;-I03,are rotated-by the shaft of the motor 82,;Fig. 9, through the angle 5, Fig. l, and are insulated from:the shaft and from each other. .As the voltage applied to-the windingB'I varies with the voltage selectedby the wiper I02 varies with "R sin 5, and the voltage selected by'the-wiper I03 varies-with R cos 6.

J Gurr-ent from the source 9 I can flow through the upper-halfpf the potentiometer winding M4 to groundythence, back to source -SI. Cur-rent can also flow from source -93 through ground to the lower half of potentiometer winding I04, thence through connection I 05 to source 93. The wipers I06, Iil'I are simultaneously -moved or manually adiusted=in opposite directions to select equalpos-itive and negative voltages with respect to ground proportional to the velocity of the vehicle 'with respect to the air, that is, the air speeds.

The positive voltage from the wiper I06 and the 11 negative voltage from the wiper I91 are applied to diametrically opposite points of a potentiometer winding I08, the equidistant intermediate points being grounded. The potentiometer winding N38 has a resistance varying with the length of the Winding such that the voltage with respect to ground varies with a sinusoidal function, and thus has the same variation of voltage with respect to ground as the winding 91. The wipers IIO, III are moved by the shaft of the servomotor of the gyroscope maintaining the fixed axis through an angle proportional to A, the wipers III], II I being insulated from the shaft and from each other. With zero angle at the points I99 and clockwise rotation, the wiper III] will select a voltage proportional to the negative cosine, and the wiper III to the positive sine of the angle of rotation. As the applied voltage is proportional to S, the voltage selected by the Wiper IIO is proportional to S cos A and the voltage selected by the wiper III is proportional to +S sin 7\.

The resistors H2, I I3 limit the currents drawn from the potentiometer winding I02, and thus make easier the design of the potentiometer wind- "In the measurement of the slant range and azimuth angle of the target, some errors are involved, The measuring process is not perfectly accurate, producing random errors in range which are roughly constant but tend to decrease slightly with decreasing range; and random errors in azimuth angle which are in the form of angular errors, but are equivalent to a linear error which also decreases roughly with the reciprocal of the decreasing range. The observers will tend to overrun and underrun the target in tracking, producing a more or less regular error, depending on the skill of the observer, and tending to decrease with decreasing range. As the measurements are expressed in the form of electrical voltages, which are conveniently selected by means of wire-wound potentiometers, there will also bea step-like error due to the sudden variation in voltage from one turn of wire to the next. These small errors in the positional measurements CHI]. produce large momentary errors in the derived ratio R. and R6, which must be averaged out, It is difficult to average or smooth an inherently variable quantity, such as R or R6, to produce the most probable value Without reducing the accuracy of the measurement. In the present computer, these inherently variable quantities are combined to give quantities which, under the assumptions usually made in bombing, should be constant. In particular, it is assumed that for some time before releasing the bomb, and during the fall of the bomb, the wind and target velocities remain constant in direction and magnitude. Thus, it is convenient and consistent to express R and R6 in terms of the assumedconstant velocity of the air with respect to the target. Rand R6 are resolved into components along the X and Y axes. By subtracting the airplanes airspeed components S cos A. and S sin A, in effect the air Velocity is determined with respect to a point fixed to the target.

The observation of the target may start when the distance is too long for reliable results. Thus, some time after the target has come under observation, the operator presses a key and the observed data are sent to the computer. Observed data are treated as above to give the components of the velocity of the air with respect to the target, and these values are electrically smoothed or averaged. As the earlier observations are not as accurate as the later observations, the averaging process is weighted approximately in accordance with an inverse range function. This result is attained by switching in added averaging elements at regular intervals as the range decreases, so that the later observations will have materially more effect on the final result than the earlier observations,

The voltage selected by the Wiper I93 proportional to -R cos 6, and the voltage selected by the wiper I I9, proportional to S cos x are supplied to the :2 wind computer, Fig. 10; the voltage se-' lected by the Wiper I02 proportional to R sin 6 and the voltage selected by the wiper I I I proportional to +8 sin A are supplied to the 11 Wind computer, Fig. 10.

In Fig. .10 the voltage proportional to S cos A is applied through connection 3I2, resistor III, and variable resistor H5, to the amplifier IIIi, which may be of the type shown in Fig. 13. The resistors H1, H8 are connected by connection H9 in serial relationship across the output of the amplifier II6, and negative feedback is supplied from the junction of resistors H1, H8, through resistor I I5 to the input of amplifier H8.

The voltage proportional to +S sin 7\ is similarly applied through connection 3I5, resistor I25, and variable resistor I2I, to the amplifier I 22, which may also be of the type shown in Fig. 13. The resistors I23, I24 are connected by connection I25, in serial relationship across the output of the amplifier I22, and negative feedback is supplied from the junction of resistors I 23, I24 through resistor I 2| to the input of amplifier I22.

The voltage proportional to R cos 6 is connected through connection 3I'3, resistor I26, capacitor I21 and connection I69 to the center armature of relay I28. Similarly, the voltage proportional td-R sin 6 is connected through connection 3M, resistor I29 and capacitor I30 to the right-hand armature of relay I28. At the start of the bombing run, relay I28 is held operated, grounding both of these armatures.

After the bombing run has started and the observations have settled down, the key I3I is operated,'releasing the relay I28; W'hen relay I28 is released, the voltage proportional to R cos 6 is supplied through resistor I26 and capacitor I21 to the input of amplifier H6; and the voltage proportional to R sin 6 is supplied through resistor I29 and capacitor I38 to the input of amplifier I22. As shown in United States Patent 2,251,973, August 12, 1941, E. S. L.

Beale et al., when a voltage is supplied through a capacitor to the input of an amplifier, the output of the amplifier will contain a component proportional to the time derivative, or rate of change, of the applied voltage. Thus, the output of the amplifier I'IB will have a component proportional to and the output of the amplifier I22 will have a component proportional to %(R sin 6) A large value of reverse feedback is supplied by the connections I I9 and I25, thus reducing the apparentinput impedances to ground of the amplifiers IIS and I22 to a very low value, increasing the-accuracy of the diiferentiating and the summing actions.

sari-stat the emitter ms txiti's the applied vtitages proportional to s (50's Xa'nd di .F k-R cost) and reverses the charit toiiioduce a Voltage proportional to l- W S-iihilarlythe amplifier I22 adds the applied images proportional to reverses the polarity to produce a voltage proportional-to'+Wy. H J

The resistors I26, I29 smooth the-applied volt- "ages. The ftimECOHStHIRESOfWhB resistor -I2 6and capacitor I21, and of the resistor I29 and. capacitor -I3Ilshou1dbe rairlysmall.

u The released-relay I28 also connectscapacitor I32 and resistor I 33 in serial relationship from the output to the input of the'a'mplifier I I6; and connects the capacitor I34 and resistor I35 in serial relationship irom the output 'to' the input of the amplifier 122. The feedbacks through capacitors -I32 and I34, integrate or average the applied voltages, though, as capacitors I32 and Is s are comparatively small, this averaging is than, 7 v

Positive volta'ge is applied from the source I35, through resistor -I3Ttoa control electrodeof the three element cold 1 cathode device I38, which "may be "a Western Electric 'jtype 313C vacuum tube. long as the relay 261's operated, the 'c'ontr'ol electrode 'is grounded through resistor I39, and th'e'ap'piied 'v'olta'g'eis too small tobreak 'do'w'nthetube. When th'erelay I26 isreleased, the voltage from thesource 1'38, through resistor -I3 l, increases thecharge on capacitor I4il, un'ti1 the voltage applied totheccntrorelectrode breaks down the tube, permitting current from the -source-l36, and the capacitor Isl to flow-through the tube I38and the Winding of relay I42, operat ing-relay I42. The-resistance of resistor-I31, and the capacitance Qfcapacitor I43 are so-related to the breakdown voltage of tube I38 that a delay of some ten seconds is'producedbetweenthe release of relay I28 and the operation oi -relay I42.

The operation of key I3I and relay I42 completes a locking circuit for relay I42 from the source I43 through the upper springs orkey'nl, left -make springs and winding of relay I42 to g-round and connects the source I43 through the upper springs of key I3I and. the right make springs of relay I42 to connection I44.

Thegrounded wiper I4-5is-r0tated by the shaft of the motor at, Fig. '1, proportionately to the horizontal range to the target. At some convenient range, the wiper I45 grounds the contac't l 46.

I When contact I46 is grounded, current can flowffrombattery I43, through key I3I, springs "orien I42, connection I44, winding of relay'I'o'I, break contacts of second spring pile-ups errelays I52, I54, I56, I58, I60 and connection I'4'I to contact I46,'operating relay II which looks up through the middle grounded make contact.

'Ih'eoperation of relay I 5| connects capacitor I'j48 and resistor [49in parallel relationship with capacitor T32 and resistor I33, increasing the loading functionof amplifier H6; "and connects capacitor IBI and resistor I62 in parallel relationship with capacitor I34 and resistor I35, in-

creasing the loading-functionbf amplifier I22.

As the rangecontinues to decrease, thewiper I45 is rotated until contact IE3 is grounded. 'Wheh cont act I63 is grounded, current can fiow from b'attcry 3 I 43, through key I3 I springs it of relay I42, connection I44, Wihairigof relay I52, break contacts of second spring pile-ups of relays I53, 155, I57, I53! and connection F64 to contact I63, operating relay 152, which, at the second. spring pile-up transfers the chain tonnection' from the'windingof'relay I5 I to the winding of relay I53 and locks up through the grounded make contact or the third pile-up.

The operation "of relay 152, at the up erspring pile-up, connects capacitor I65 and resistor in parallel relationship with capacitor I32 and resistor I33; and,at the lower spring piie-up'con- -nects capacitor I 5 and resistor I68 in parallel relationship with capacitor I34 and resistor I35.

'The continued rotation of Wiper I45 causes the operation ofthevremaining chain relays I53 to I60, in succession, until the bomb has been released, or minimum range is reached.

The successive operations ofthe chain relays I53 to I66 connect a succession of capacitors'and resistors in paralle'l relationship with capacitor I32 and resistor I33,-a'hd in parallel relationship with capacitor I and resistor I35, thus progressivel'y changing the ayeragingiproperties of ampl-ifi e'rs I I6 and -I22. The resistors may con- 'veniently be'of about 10,000 ohms,=capacitors 132, -I -34-:about 1 microfarad'each, capacitors I48, -I- 6I 'about I .25 microfarad eachand'the -remainin-g ca,-

pacitors, such as I65, I61, about .35 microfarad aeh- When the bombing run is completed, the release of key I3'I unlocksrelay I42 and all the chain relays I 51 to (to which maybe-locked up, and operates relay I28, restoring the circuit to its initial condition "inprepa'ration for the next bombing run.

The quantity WK '(and the quantity "We a :velocity; thusfthewighted average ofthis velocity is, by definition:

I a Fdt -in "which "this the time at'which the averaging process 'startsgand F is the weighting-function. By'ev'aluatin'g the timerate orchange or T; of Wx from the above equationjthe equationmaybe manipulated into the difierential form:

'W, W,,KW,,=O in which K usually varies with time, and,

I Let C1 be the capacitance of capacitor I21, Cz be the-capacitanc'e'of the'capacitors, such as capacitor I32, in the feedback path, R1 be the resistance of resistor II 'I, the Voltage gain of amplifier I'I '6, Mbe large and substantially'inde- *pendent of "frequen'cy,the' outputload of amplifier 1H3 be a substantially constant resistance, 'an'the internal output impedance of amplifier IIG be small compared withtheresistance "Ri'in parallelrelationship withbz. Under-these conditionsQthe total impeuanee'zt fromthe output terminalof amplifier I I6 to ground is "approximately representedby a capacitance Ct in parallel relationship with a resistance Rt.

The constants of the circuit of Fig. 11 are adjusted to produce scale factors such that the voltage selected by the wiper I03 is K1 R cos 6, and the voltage selected by the wiper III! is R2C1 K1 S cos X, where K1 is a constant.

Including these limitations, the output of amplifier I I6, equal to K2 Wx, obeys the following equation:

which is equivalent to Equation 11 if The capacitors, such as capacitor I48, are connected to the output circuit of amplifier II6, so that they will be charged up to the output voltage, and are switched, at the low potential side, from ground to the input of amplifier II6, so as to avoid causing spurious discontinuities in the value of VVX.

With C2 increased by discrete steps, the weight function increases exponentially with time between charges, With exponent inversely proportional to the value of C2, and abruptly decreases when a new value of capacity is switched in. These abrupt changes are smoothed out, by the series resistors, such as resistors I26, I29.

The complete circuit produces a result that closely approximates to a weight function which is zero before time to and increases thereafter with the reciprocal of the horizontal range.

The amplifiers I I6 and I22 reverse the polarities of the applied voltages. Thus, as the input to the amplifier H6 is proportional to W,:, the output of amplifier H6 is proportional to +Wx; and the output of amplifier I22 is proportional to +Wy.

The output voltage of amplifier I6 is supplied by connection 3I6 to the point I10 of the potentiometer winding I1I, Fig. 11. A portion of the and output of amplifier H6 is supplied, through con-' nection 3I I and resistor I12, to a summing amplifier I13, which may be of the type shown in Fig 7 13, having a feedback resistor I14. The amplifier I13 reverses the polarity of the applied voltage. The output of the amplifier I13, which is proportional to Wx is supplied to the point I15 of the potentiometer winding I1I.

The potentiometer winding I1I, like the windings 91 and I88, has a resistance varying with the length of the winding such that the voltage with respect to ground varies with a sinusoidal function. With zero angle at the point I16, and clockwise rotation, the wiper I11 selects a voltage proportional to a negative sine, and the wiper I18 selects a voltage proportional to a positiveccsine. The wipers I11, I18 are moved by the shaft of motor 82, Fig. 9, an angle equal to angle 6, Fig. 1, the wipers I11, I18 being insulated from the shaft and each other. The voltage selected by the wiper I11 is thus proportional to WX sin 6 and the voltage selected by the wiper I18 is proportional to +Wx cos 6.

The output voltage of the amplifier I22, Fig. 10, proportional to +Wy is supplied by connection 3I6 to the point I80 of the potentiometer winding 16 I 8|, which has a variation in resistance similar to the variation in resistance of the winding IN.

The output voltage of the amplifier I22, Fig. 10, is supplied by connection 3I1 to the input resistor of amplifier I82, and the polarity of this voltageis reversed in the amplifier I82, which is similar to amplifier I13 and supplied to the point I83 of the Winding I8I.

With zero angle at the point I 84 and clockwise rotation for increasing angles, the wipers I85 and. I86 respectively select voltages proportional to a positive sine and a positive cosine. The wiper I85 is therefore displaced 180 degrees with respect to wiper I11. The wipers I 85, I86, like the Wipers I11, I18, are moved by the shaft of motor 82, Fig. 9, an amount proportional to angle 6, Fig. 1, and are insulated from the shaft and from each other. The voltage selected by the wiper I85 is thus proportional to +55 sin 6 and the voltage selected by the wiper I86 is proportional to Vl iy cos 6.

The voltages selected by the wipers I06, I01, respectively proportional to +8 and S are supplied, through resistors I I2, I I3, to points I81, I88 of potentiometer winding I89. The winding I89, like windings 91, I08, HI and I8I, has a resistance varying so as to produce a voltage varying with a sinusoidal function. The Wipers I90, I9I are moved by the support 23, Fig. 6, an amount proportional to the angle 0,.Fig. 1. With zero angle at point I92 and clockwise rotation for increasing angle, the wipers I90, I9I respectively select voltages proportional to +3 sin 0 and -S cos 0.

Thevoltage selected by thewiper I11, proportional to Wx sin 6; the voltage selected by the wiper I proportional to +8 sin 0; and the voltag e selected by the wiper I86 proportional to +W cos 6 are respectively supplied, through re- 8 sisters I93, I94, I95 to the input of a summing amplifier I96 which may be of the type shown in Fig. 13, having a feedback resistor I91. The summing amplifier I96 sums up the voltages +8 sin 0-7 sin 6+l V,, cos 6 which, from Equation 8 are equal to As th amplifier I96 also reverses the polarity of the applied voltages, the potential of the connection I98 with respect to ground is proportional to The voltage selected by the wiper I18, proportional to +W'x cos 6; the voltage selected by the wiper I9I, proportional to S cos 0; and the voltag e selected by the wiper I85 proportional to +Wy sin6 are respectively supplied through resistors I99, 200, 20I to a summing amplifier 202, similar to amplifier I96 and having a feedback resistor 293. The amplifier 282 sums up the voltages 17 plus or minus 90 degrees, because, if the angle 0 exceeds 90 degrees the vehicle would be flying away from the target.

The angle 0 is thus always in the first quadrant, where the sine and cosine are of the same sign, or in the fourth quadrant where the cosine is unchanged, but the sine changes sign. In a potentiometer having only one wiper arm, the winding may be spread over the whole circle, the wiper arm being moved through 20. For a cosine function, the voltages applied to the two halves of the winding are of the same polarity. For a sine function, the voltages applied to the two halves of the winding are of opposite polarity. In a potentiometer having two wiper arms, the winding may extend over the whole circumference, or may be limited to three quadrants extending over the circumference, the arms being geared to rotate through 3/20.

The potentiometer winding 205 has a resistance varying with a cosinusoidal function in the first and fourth quadrants, the zero angle or axis of the vehicle being at the point 206. The wiper 201 is driven by the support 23, Fig. 6, at twice the rotational speed of the support 23, say by means of suitable gearing. The voltage of the connection I98 is applied at the point 266. The voltage selected by the wiper 287 will be proportional to R6 cos 0 The potentiometer winding 208 has a resistance varying with a sinusoidal function in the first and fourth quadrants, the zero angle being at the ground. The voltage of the connection 284 is applied directly to the upper part of the Winding 208. The voltage of the connection 264 is applied through a resistor 209 to an amplifier 2 II], which may be of the type shown in Fig. 13, having a feedback resistor 2I I. The amplifier ZIO reverses the polarity of the voltage of the connection 204, and supplies voltage of reversed polarity to the lower half of the winding 208. The wiper 2I2, like the wiper 201, is moved through twice the angle of the support 23, though both wipers are insulated from the drive and each other. The wiper 2I2 will select a voltage proportional to R sin 6 The voltages selected by the Wipers 201 and 2 I2 are respectively supplied through resistors 2I3, 2 I 4 to an amplifier 2 I 5 of the type shown in Fig. 14 which adds these voltages and reverses the .po-

larity. The output voltage of amplifier 2I5 tends to be proportional to RS cos 0+R sin 0 which is the component of the ground speed V transverse to the course of the airplane.

The output voltage [of the amplifier 2I5 is supplied to the winding of a potentiometer 2 I6 having 18 E2 will appear in the output circuit and this voltage is applied across the winding 2 I6. The wiper 2I1 selects a voltage R132. Let the resistor 2I8 have a resistance R2. Then the current I2 in the resistor 2 I 8 equals RE, E,

The effect of high negative feedback is to keep E0=O. Hence, since I1=-I2 of the sum of the input voltages. If the resistors R1 and R2 are not equal, the output voltage is changed in the ratio of R2 to R1. The output voltage is also reversed in polarity.

The output voltage of the amplifier 2I5, proportional to dt sin 0+5 cos 6) is applied to a potentiometer winding M9. The wiper 220 is adjusted to select a voltage proportional to the value of the trail T for the partitcular speed and altitude of the vehicle. The wiper 220 will thus select a voltage proportional to gd fi sin 0+5 cos 0) This voltage is supplied to the steering circuit 22I, together with a voltage from the connection I98 equal to The steering circuit 22l, and the amplifier 2I5, shown in Fig. 12, produce a current proportional to the difference of the imput voltages g6; sin 6+ cos 0) (-755) which may be written his (Fa cos 0+5 sin a as in Equation 1. The output current of the steering circuit 22l actuates the meter 222. When the vehicle is on the correct course, the meter 222 reads in the center of the scale. When the vehicle is off the correct course, the meter 222, which has a center zero, indicates the direction and magnitude of the amount off course. Thus,

as the vehicle approaches the release point the pilot steers the vehicle to keep the meter 222 reading zero.

Voltage from the connection 204, Fig. 12, proportional to is applied to the potentiometer winding 223. The wiper 224 is adjusted to select a voltage proportional to the time fall 25 for the particular altitude of the vehicle. The voltage selected will be proportional to A source of voltage 225 has the negative pole connected to one endof the potentiometer winding 226. The other end of the winding i226 and the positive pole of the source 225 .are grounded. The wiper 221 is adjusted to select a voltage proportional to the proper trail T ,for the speed and elevation of the vehicle. This voltage is applied to the mid-point of the potentiometer winding 223 which is similar to the winding 26.5. The wiper 229, like the wiper 261, is moved proportionally to the angle 0, and is insulated from the drive shaft. The wiper 229 thus selects a voltage proportional to T cos 6. The wiper 221, and the wiper 220 may be ganged to move simultaneously.

The source of voltage 225 also has the negative pole connected to a potentiometer winding 232.

The other end of winding 230 is grounded. The wiper 23! is moved by the motor 46, Fig. '7, proportionally to the horizontal range .to select a voltage proportional to R. The wiper 23| is insulated from the drive shaft.

The voltage selected by the wiper 224, proportional to it the voltage selected by the wiper 229, propor- ..ti onal to -T cos 0; and the Voltage selected by the wiper 23l, proportional to R are respectively supplied, through resistors 232, 233, 234, to the release circuit 235, which may be of the type shown in Fig. 15, and which sums up the applied voltages. The output of the release circuit 235 to thus proportional to rect release point.

The summing amplifiers 6, I22 of Fig. 10; I13, I82, I96, 202 of Fig. 11 and 2H], of Fig. 12 may .all heal the type shown in Fig. 13.

In Fig. 13, the signal voltages are applied to the control grid-of the upper section of the twin vacuum tube 240; The source 24! supplies anode current through. the coupling resistor 242. The source 243 supplies current to the anode of the lower section, which is connected so-as to reduce drift due to variations in cathode activity as described in an article Sensitive D. C. Amplifier with A. 0. Operation by S. E. Miller, published in Electronics, November 1941, page 27. The combined anode currents flow through the resistor 244, which is of fairly high resistance. The source 245 impresses a potential with respect to ground which opposes the potential due to the voltage drop in the resistor 244. The resistor 244 may be varied to adjust the space currents difference between the control grid and cathode of the vacuum tube 246 is of suitable value;

The vacuum tube 246 is coupled to the vacuum b 241 y an nt sta e network of the type shown in United States Patent 1,751,522, March 25, 1930, H. Nyquist. The anode circuit is supplied from the source 24l, and the grid bias from the source 2.45. The vacuum tubef241 is coupled '20 to the vacuum tube 248 by a similar interstage coupling network.

A portion of the output voltage of the vacuum tube 245 is tapped at the point 249 and supplied to the grid of the vacuum tube 250. Thus, the direct signals are supplied to the grid of vacuum tube 250; while vacuum tube 241 acts as a phase inverter and amplifier to supply signals of reversed polarity to the grid of vacuum :tube 248.

The control grids of the vacuum tubes 241, 250 are biased to a fairly high negative voltage with respect to ground, and this voltage is largely compensated by a negative bias applied to the cathode of the Vacuum tubes 241, 250 by the source 25L Positive potential from the source 243 issupplied by connection 253 to the anode of vacuum tube 248. The cathode of vacuum tube 248 is connected to terminal 252 and to the anode of vacuum tube 250. The cathode of vacuum tube 259 is connected to the negative pole of the source 25L The positive pole of source 25l and the negative pole of source 243 are grounded. If the vacuum tubes 248 and 250 have the same anode-cathode resistance, and the sources 243, 25! are of the same potential, or if the ratio of the anode-cathode resistances of the vacuum tubes 248, 256 is the same as the ratio of the potentials of the sources 243, 251, these four elements will form a bridge, and in the absence of an applied signal the terminal 252 and ground are conjugate to each other, that is, the terminal 252 is at ground potential.

If a negative signal voltage be applied to the control grid of the vacuum tube 250, an inverted signal will be applied to the vacuum tube 248, the anode-cathode resistance of vacuum tube 250 will increase and the anode-cathode resistance .of vacuum tube 248 will decrease, thus unbalancing the bridge and causing a potential to appear at the terminal 252. To counteract the tendency of this potential toward diminishing the response .of tube 248, the signal voltage applied to the grid of this tube must be larger than that applied to the grid of tube 250. This condition is brought about by the amplification in the stage which includes tube 241.

The screen grid of tube 248 is connected to source 24! and the screen grid of tube 250 is connected to source 243. The cathodes are heated in known manner (not shown).

Using commercial radio receiving tubes, the source 24! may be about positive 270 volts, the source 245 about negative 270 volts, the source 243 about positive 100 volts and the source 2'5I about negative 100 volts, all with respect to ground.

A negative voltage applied to terminal 254 will decrease the anode-cathode current of tube 240, decreasing the voltage drop in resistor 242, increasing the positive potential of the control grid of tube 246. Increasing the positive potential of the grid of tube 246 will increase the anodecathode current, increasing the voltage drop in the coupling resistors, and reducing the positive potential applied to the control grid of tube 241, and of point 249 connected to the control grid of tube 250. As a reduction of positive potential is equivalent to an increase of negative potential, the variation in :potential of the control grid of tube 250is of the same polarity as the voltage applied to the terminal 254. An increase in negative potential on the grid of tube 241 reduces the anode-cathode current, reducing the voltage rop in, the coupling resistors .and increasing the positive potential of the grid of tube 248. The

increased negative potential on the grid of tube 259 will reduce the anode-cathode current while the increased positive potential on the grid of tube 248 will increase the anode-cathode current; thus, current will flow from terminal 252 through an attached load to ground. Thus, if a negative voltage is applied to terminal 259, a positive voltage appears on terminal 252, or the polarity of the applied signal is reversed by the amplifier.

When a feedback resistor is connected between terminal 252 and terminal 254 and a plurality of voltages are applied through individual resistors, as shown, for example, in connection with repeaters I96, 262, Fig. 11, the negative feedback will reduce the apparent input impedance of the repeater to a very low value, so that the various sources do not interact on each other, and the gain of the repeater, for any given source, will be controlled by the ratio of the resistance in the feedback path to the resistance in series with the source. The summing amplifier 2l5 and steering circuit 22! of Fig. 12 are shown in detail in Figs. 14 and 14A.

The resistors 2l3, 2H1, Fig. 12, are connected to terminal 255, Fig. 14, which is connected to the control grid of the lower section of the twin triode 256. The positive pole of a voltage source 251 is applied to the anode of this section. The cathode of the tube is connected through a resistor 258 and a negative voltage source 259 to ground. The control grid of the upper section is connected to ground, and current from a positive voltage source 269 is supplied through resistor 26l to the anode of the upper section. Assume a negative voltage is applied to terminal 255, decreasing the anode current of the lower section and decreasing the voltage drop in resistor 258. The cathode of tube 256 then has a negative potential with respect to ground, which is equivalent to a positive potential on the control grid of the upper section. The lower section of tube 256 thus operates as an inverter to impress on the control grid of the upper section a voltage having a polarity which is reversed with respect to the applied voltage. The polarity is again reversed in the upper section so that the voltage on the grid of the tube 262 is of the same polarity as the signal. This voltage is again reversed by the tube 262 so that the voltage on the grid of vacuum tube 263 is of a polarity reversed with respect to the applied signal.

The cathode of vacuum tube 263 is connected to ground through the potentiometer windings 216, 2I9, Fig. 12, in parallel relationship.

The negative pole of voltage source 259 is connected through resistor 264 to the cathode of vacuum tube 263. The positive pole of the source of voltage 269 is connected by connection 265 directly to the anode of vacuum tube 263. The positive pole of voltage source 259 and the negative pole of voltage source 269 are grounded.

The resistance of the resistor 26 i is selected so that, in the absence of an applied signal, the sources 259, 269, the resistor 26 and the anodecathode resistance of vacuum tube 263 form a balanced bridge; thus point 266 is conjugate with respect to ground and no voltage is applied to windings 216, 219.

Assuming a negative voltage to be applied to terminal 255, this will cause a positive voltage to be applied to the control grid of the vacuum tube 263, increasing the anode-cathode current of vacuum tube 263 and unbalancing the bridge.

'The point 266 will become positive with respect to ground, that is, the wiper 2l1 will become positive with respect to ground. Wiper 211 is connected by terminal 261, through resistor 2I8, Fig. 12, to terminal 255 and the control grid of vacuum tube 256. Thus, a negative voltage with respect to ground applied to the control grid of vacuum tube 256 produces a voltage on wiper 2l1 which is positive with respect to ground, and this voltage is applied to the same control grid, forming a reverse or negative feedback.

The unbalance voltage between the point 266 and ground, due to a voltage applied to terminal 255, is also applied to the potentiometer winding 219, shown in Fig. 12. The voltage selected by the wiper 229 is applied to the control grid of vacuum tube 268.

The voltage from the connection I98, Fig. 12, is applied through terminal 269 to the control grid of a vacuum tube 219'.

Positive voltage from the source 269 is supplied by connection 265 through resistors TN, 212 to the anode of vacuum tube 268 and through resistors 213, 219 and meter 215 to the anode of vacuum tube 219.

The cathodes of vacuum tubes 268, 219 are connected through resistor 216 and a negative voltage source 211 to ground and the negative pole or source 269. The anode-cathode resistances of the vacuum tubes 268, 219 with resistors 21!, 212, 213, 214 and meter 222 form a bridge which, in the absence of a signal voltage, is balanced. The meter 222 has a center zero for normal value of anode current in vacuum tube 219 and this zero may be accurately set by adjusting resistor 21 5.

Assuming that vacuum tubes 268 and 219 are of the same type, having the same mutual conductances and internal impedances; that the product of the mutual conductance of a tube and the internal impedance is large compared to unity; that the product of the mutual conductance of a tube and the resistance of resistor 216 is also large compared to unit; that the resistance of resistors 21I, 212 equals the resistance of resistors 213, 214, and is large compared to the in ternal impedance of the tubes, then, it may be shown that the unbalance voltage sending current through 213, 214, and meter 222 equals vi-v2) where g is mutual conductance of tubes,

R1 is internal impedance of tubes,

R is resistance of resistors 21! and 212, V1 is voltage applied by wiper 229,

V2 is voltage applied by terminal 269.

The voltage applied by the wiper 229 is proportional to %(;3; cos 0+1? sin 0) and the voltage from connection I98, Fig. 12, ap-

se'ctioncf vacuum tube 282 is :thusproportional'to and this negative voltage on the control grid of vacuum tube 282, reduces the anode current of vacuum tube 282 to a small value. The anode current of vacuum tube 282 issupplied by,voltage source 283 through the anode coupling resistor 284. The lower section of the twin triode vacuum tube 282 is connected like the lower section of vacuum tube 249, Fig. 13, to compensate for cathode temperature drift.

The voltage applied to terminal 288 is amplified by the upper sections of the twin triode vacuum tubes'282, 281 and supplied to the control electrode of the gas-filled triode 289. A positive voltage from the source 299 is applied to the cathode of the gas-filled triode 289, to produce a negative bias on the control electrode. The negative bias from the source 290, with the negative amplified signal, holds the tube 289 inoperative until the amplified signal .falls to zero, reducing the negative bias on the control electrode of the gas-filled triode 28.9 and permitting the tube to fire.

Current from the source 283 is supplied by connection 29L key 292 and resistor 293 to charge capacitor 294. When the gas-filled tube 289 fires, the capacitor 294 discharges through the relay or latch winding 236 and tube 289, energizing the winding 236 and releasing the bomb. The discharge of capacitor 294 permits cur-rent to flow from source 283 through resistor 293, causing a voltage drop across resistor 293 which lights a small neon lamp 295, or other indicator,

to indicate the release of the bomb. Upon completion of the bombing run, when the control electrode of the gas-filled triode 289 is again biased negatively, the key 292 is operated, breaking the circuit from the source 283 and permitting the tube 289 to restore.

The voltage applied to the terminal 289 releases the bomb when which is the correct release condition, but if no precautions were taken, the bomb might be released when the airplane was not headed properiv. The steering circuit of Fig. 14A is arranged to block the bomb release circuit of Fig. 15 at all times when the airplane is off the correct track.

The anodes of a double diode vacuum tube 296 are connected to the outer ends of the resistors 21!, Fig. 14A. The outer ends of two equal resistors 291, 219 are also connected respectively to the anodes of tube 298. The junctions of resistors 291, 219 are connected through resistor 293 to the cathode of tube 296.

When the airplane is on the correct track, equal voltages are applied to the control electrodes of vacuum tubes 288, 218, and assuming the resistances of resistors 212, 214 are equal and the resistances of resistors 21!, 213 are'equal,

equal voltages are applied to the anodes of tube As the resistors 291, 219 are equal, no current flows in tube 296. When the airplane is off the correct track, the voltages applied to the control grids of the vacuum tubes 268, 210 are not equal, and the anode-cathode currents are not equal. Assume the anode-cathode current of tube 288 to decrease while the anode-cathode current of tube 218 increases. The decreased current in resistor 21| will permit the positive potential of the outer end of resistor 21! to rise,

24 while-the increased current in resistor 21 3 will causethe positive potential of the outer end of resistor-2:13 to fall. Current can then fiow from the lower anode of tube .296 to the cathode and through sresistors .298, 291.

Similarly, when the anode-cathode current of tube 268 increases while the anode-cathode current of tube 210 decreases, then current can fiow from the upper anode of tube 296 to the cathode and through resistors 298,219. Thus, whenever the air'planesis Iofi the correct track, the cathode :of tube'2 961andthe free end of resistor 298 beoom'emorepositive with respect to ground. This potential will appear on terminal 299, which is connected to terminal 300, Fig. 15.

Terminal 300 is connected through resistor 30"! to a resistor 382 connected to the control electrode :of the lower section of the twin triode 281.

'The negative pole of the voltage source 288is also connected through resistor 393 to resistor 302. The potential of source 288 is selected so that, when the airplane is on course, the anode-cathod'e'curren t of tube 281 is small. When the-airplane is off course, the positive potential develope'd'across resistor 298, Fig. 1 4A, is applied through resistors 39!, $82 to the control electrode of the lower section of tube 281, and causes the .an'odeecathode current of tube 281 to increase.

'The source 299 is connected through the winding of relay 8 94 to the 'anode of the lower section of tube 281. When the airplane is on course, the anode-cathode current of tube '281is too small to operate relay 384. When the airplane is on the correct track, this anode current increases,

operating relay 394 and connecting negative volt- 'agezfrom the source 2 85 to the control grid of the gas-filled triode .2 89, preventing the triode 289 from firing and releasin the bomb. Thus, even if the release voltages have fallen to the correct value, the bomb cannot be released, unless, at the same time, the airplane is on the correct track.

What is claimed is:

1. In combination, a pair of similar thermionic devices, each having a cathode, an anode and a control electrode, said cathodes being directly connected, :a first grounded source of voltage of negative polarity, a first resistor connecting said first source to said cathodes, a second grounded source of voltage of positive polarity, a second resistor connecting said second source to one of said anodes, a third resistor, an ammeter, means connecting said third resistor and said ammeter in serial relationship from said second source to the other of said anodes, the resistances of 'said third resistor "and said ammeter'being approximately equal to the resistance of said second resistor, a third source of voltage of one polarity connected to the control electrode associated with said one anode, a fourth source of voltage of opposite polarity to said third source connected to the control electrode associated with said other anode whereby for approximately equal values of and approximately equal variations in said third and fourth voltages, the reading of said meter is substantially unchanged.

2. In a system for guiding an aerial vehicle along the track through the correct point at which to release a bomb to strike a target, a first measuring means including a first shaft rotated proportionately to the azimuth angle between the axis of the vehicle and the vertical plane through the vehicle and the target, a second measuring 75 means including a second shaft rotated proportionately to the horizontal range to said target, a first potentiometer having a winding varying in resistance with a sinusoidal function and a first wiper moved by said first shaft, a first source of voltage varyin with the rate of change in the horizontal range to said target connected across the winding of said first potentiometer, a second potentiometer having a winding varying in resistance with a cosinusoidal function and a second wiper moved by said first shaft, a second source of voltage varying with the transverse component of the relative velocity of said vehicle and said target connected across the winding of said second potentiometer, a thermionic amplifier having an input and an output circuit, means for Supplying the voltage selected by the wipers of said first and second potentiometers to the input circuit of said amplifier, a third potentiometer having a winding connected across the output of said amplifier and a wiper moved by said second shaft, means for feeding back the voltage selected by the wiper of said third potentiometer to the input of said amplifier, a fourth potentiometer havin a winding connected across the output of said amplifier and a wiper adjusted to the known value of the trail for said bomb, and a differential meter for comparing the voltage from said second source with the voltage selected by the wiper of said fourth potentiometer whereby equality of said voltages indicates the correct track for said vehicle.

3. In a system for indicating when a bomber is on the track through the point at which a bomb, when released will strike a target, a source of energy, mechanism connected to said source and controlled in accordance with observations of the target to produce from said source first and second quantities of energy respectively proportional to the component of the ground speed of the bomber normal to the vertical plane containing the axis of the bomber, and to the component of the ground speed of the bomber normal to the vertical plane through the bomber and target, and including a shaft rotated proportionally to the horizontal distance between the bomber and the target, an amplifier having an input circuit connected to said mechanism to amplify said first quantity of energy and an output circuit, means connected to said output and said input circuits and controlled by said shaft to feed back energy proportionally to said horizontal distance, other means connected to said output circuit and adjusted to fractionate the output energy of said amplifier proportionally to the trail of the bomb, and meter means con-. nected to said mechanism and said other means to oppose said second quantity of energy to said fractionated quantity of energy whereby equality of said quantities of energy indicates the bomber is on the correct track.

SIDNEY DARLINGTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,573,850 Naim'ann Feb. 23, 1926 2,297,543 Eberhardt et al. Sept. 29, 1942 2,317,419 Taylor et a1. Apr. 27, 1943 2,401,779 Swartzel, J'r. June 11, 1946 FOREIGN PATENTS Number Country Date 511,175 Great Britain 1939 

